1. Field of the Invention
This invention relates broadly to apparatus and methods for the precision measuring and finishing of surfaces. More particularly, this invention relates to precision measuring and finishing of diamond surfaces using lasers.
2. State of the Art
Diamond has exceptional hardness, thermal conductivity, electrical insulation and light transmission properties, and is therefore useful in various applications such as cutting tools, heat sinks, insulators, electronic substrate materials, etc. In particular, while the use of diamond in cutting tools has been long known, it has only recently become increasingly common. Diamond cutting tools usually appear in one of three general forms: sintered cutting tools, single diamond cutting tools, and chemical vapor deposition (CVD) diamond coated cutting tools. Specific examples of diamond cutting tools include flat cutting tools for lathes, and round cutting tools such as routers, drills, and milling bits. The above-mentioned tools, however, suffer from various drawbacks. Sintered cutting tools in general have poor durability, as they contain a bonding material having inferior wear resistance and thermal conductivity relative to diamond. Single diamond cutting tools require the use of a large stone which, whether natural or artificial, can be very costly. CVD diamond cutting tools often experience separation of the diamond from the tool during cutting operations, as the adherence between the metallic substrate and the diamond coating is generally poor.
Known methods of improving the adhesion between a diamond film and a cutting tool involve cutting a diamond film produced by a vapor phase synthesis process to the desired shape and affixing it to the cutting tool, or interposing a bonding layer between the substrate and the surface diamond. Diamond film formed by vapor phase synthesis, however, tends to have large surface irregularities, and a process for smoothing or polishing (known as ablating) the surface of the diamond film is required to obtain the proper thickness tolerance and surface finish. Due to the extreme hardness of diamond, specialized tools are required for accurately measuring and machining the surface of the diamond film to the desired finish. Typical methods for mechanical diamond finishing involve abrading the diamond film with a diamond grit slurry on a lapping machine. These methods tend to be costly and time consuming, however, often entailing ablating speeds of about 0.1 .mu.m/min to 0.1 .mu.m/hr and requiring up to several weeks to finish a four inch diameter diamond wafer.
In order to overcome the aforementioned shortcomings of conventional diamond film ablating methods, it is known in the art to use a laser or other high energy beam to ablate the surface of a diamond film in order to achieve a desired finish. The use of lasers and similar high energy beams is usually less time-consuming and more accurate, as well as more cost efficient than conventional mechanical processes. In general, laser ablation is accomplished by irradiating the surface of the diamond with a laser beam at an angle, such that the convex irregularities on the surface are exposed to a higher laser power density than the planar areas, and the concave irregularities are shielded by the convex ones. The laser undergoes several passes over the surface of the diamond to evenly smoothen the surface. The result is that a maximum convexity height (Rmax) of 50 .mu.m on the surface of a diamond can be reduced to 3 .mu.m within a short period of time.
A problem with known laser ablation techniques, however, is that it is difficult to obtain any particular level of surface smoothness unless the surface of the diamond film is ablated in very small increments and separately measured after each ablatement. This process is time consuming, especially in light of the fact that the diamond film must be moved and recalibrated each time it is measured or ablated.
The preferred instrument for measuring the thickness and surface finish of a thin material is one which reflects a laser beam off the surface of the material to be measured. Such an instrument is known as a "laser profilometer" and measures the surface profile of the material. The measured profile can then be related to a substrate baseline to obtain a thickness measurement for the material.
Although the use of lasers to measure and ablate diamonds has greatly improved the finishing of diamond surfaces, existing methods and apparatuses using laser technology are still too slow and inefficient to meet the increasing demands of today's industry.